Idris O. Raji

Neural stem cells, the source of newborn neurons in the adult hippocampus, are intimately involved in learning and memory, mood, and stress response. Despite considerable progress in understanding the biology of neural stem cells and neurogenesis, regulating the neural stem cell population precisely has remained elusive because we have lacked the specific targets to stimulate their proliferation and neurogenesis. The orphan nuclear receptor TLX/NR2E1 governs neural stem and progenitor cell self-renewal and proliferation, but the precise mechanism by which it accomplishes this is not well understood because its endogenous ligand is not known. Here, we identify oleic acid (18:1ω9 monounsaturated fatty acid) as such a ligand. We first show that oleic acid is critical for neural stem cell survival. Next, we demonstrate that it binds to TLX to convert it from a transcriptional repressor to a transcriptional activator of cell-cycle and neurogenesis genes, which in turn increases neural stem cell mitotic activity and drives hippocampal neurogenesis in mice. Interestingly, oleic acid-activated TLX strongly up-regulates cell cycle genes while only modestly up-regulating neurogenic genes. We propose a model in which sufficient quantities of this endogenous ligand must bind to TLX to trigger the switch to proliferation and drive the progeny toward neuronal lineage. Oleic acid thus serves as a metabolic regulator of TLX activity that can be used to selectively target neural stem cells, paving the way for future therapeutic manipulations to counteract pathogenic impairments of neurogenesis.

Lipid nanoparticles (LNPs) have great potential to enable inhaled delivery of mRNA to treat pulmonary diseases. However, this potential has been limited by the challenge of nebulizing the LNPs. Nebulization of LNPs can cause LNPs to aggregate and release encapsulated mRNA, limiting their delivery efficacy. To overcome this challenge, LNPs are developed whereby the PEG-lipid is fully replaced with a zwitterionic polymer (ZIP)-lipid conjugate to greatly enhance the nebulizer stability. LNPs formulated with ZIP-lipids (ZIP-LNPs) were stable to nebulization across a wide range of formulation parameters. The optimized ZIP-LNP formulation, containing reduced cholesterol content relative to traditional PEG-lipid LNPs, demonstrated improved inhaled mRNA delivery in both healthy and mucoobstructed mouse lungs. Repeat administration of the optimized ZIP-LNP formulation was well tolerated and did not result in pulmonary inflammation. This study demonstrates the potential of zwitterionic polymer-lipid conjugates for improving the performance of inhaled mRNA-LNP formulations.